John Mayer Doesn't Kiss and Tell About Katy Perry on 'Ellen'

What exactly made pop stars Katy Perry and John Mayercall it quits? Mayer dodged questions about the break-up on Ellen, stating:

"Listen, it was a very private relationship going in. It was a private relationship during, and it's a private relationship, still. I can understand asking the question based on some previous answers I have given, but I have finally learned how to put the wall between one thing and the other. I've been much happier since then. I'm on the same journey as everyone else. Coupling is a tricky thing."